
1. Field of the Invention
The present invention relates to a method and an apparatus for cooling a mold when a cavity of the mold is filled with molten metal to perform casting.
2. Description of the Related Art
A casting method for obtaining a cast product having a desired shape has been hitherto performed by charging molten metal into a cavity formed in a mold and solidifying the molten metal. In this process, a cooling apparatus is usually provided in order that the molten metal charged in the cavity is smoothly solidified and the mold is cooled.
FIGS. 14 to 17 show a cooling apparatus concerning the conventional technique for casting a cast product having a bottom-equipped cylindrical configuration.
The cooling apparatus 1 comprises a core pin 3 which has a hollow section 2 formed at the inside, a supply tube 4 which faces the hollow section 2 and which supplies cooling water to the hollow section 2, and a discharge port 5 which communicates with the hollow section 2 and through which the cooling water stored in the hollow section 2 is discharged.
Reference numeral 6 indicates the cast product cast by using an unillustrated mold.
FIGS. 14 and 15 are illustrative of a case which adopts the core pin 3 having a lateral typeicooling structure. FIGS. 16 and 17 are illustrative of a case which adopts the core pin 3 having a vertical type cooling structure.
FIG. 18 shows the relationship between the temperature and the flow rate of the cooling water, obtained when the continuous casting is performed by using the cooling apparatus 1 concerning the conventional technique.
In FIG. 18, a solid line (1) indicates the change of the flow rate obtained when the flow rate of the cooling water supplied to the cooling apparatus 1 is constant at a flow velocity of 1.1 liter per minute. A solid line (1)xe2x80x2 indicates the temperature characteristic of the mold obtained when the flow velocity is constant at 1.1 liter per minute. The solid line (1)xe2x80x3 indicates the temperature characteristic of the cooling water obtained when the flow velocity is constant at 1.1 liter per minute.
In FIG. 18, a broken line (2) indicates the change of the flow rate obtained when the flow rate of the cooling water supplied to the cooling apparatus 1 is constant at a flow velocity of 1.6 liter per minute. A broken line (2)xe2x80x2 indicates the temperature characteristic of the mold obtained when the flow velocity is constant at 1.6 liter per minute. The broken line (2)xe2x80x3 indicates the temperature characteristic of the cooling water obtained when the flow velocity is constant at 1.6 liter per minute.
In FIG. 18, when the casting is continuously performed, then the Nth casting is indicated by xe2x80x9cNthxe2x80x9d, and the followings are continuously represented by xe2x80x9c(N+1)thxe2x80x9d, xe2x80x9c(N+2)thxe2x80x9d, and xe2x80x9c(N+3)thxe2x80x9d.
However, the cooling apparatus 1 concerning the conventional technique involves such an inconvenience that the cooling water is evaporated during the casting due to the difference between the volume in the hollow section 2 and the flow rate of the cooling water supplied from the supply tube 4. As a result, the cooling ability is lowered due to the steam generated in the hollow section 2.
That is, an inconvenience arises such that a space 7 is formed by the layer of air and steam generated on the upper side of the hollow section 2. Consequently, the cooling becomes uneven, and the cooling efficiency is lowered. For example, as depicted by the solid line (1)xe2x80x3 in FIG. 18, in the (N+3)th casting, the temperature of the cooling water, which is obtained at the flow velocity of 1.1 liter per minute, exceeds 100xc2x0 C., and the cooling water is converted into steam.
The decrease in cooling ability causes the following inconvenience. That is, an overheat portion 8 suffers occurrence of the so-called sink mark which badly affects the cast product and the so-called capture in which a surface portion of the cast product adheres to the mold. For example, as depicted by the solid line (1)xe2x80x2 in FIG. 18, in the (N+3)th casting, the temperature of the mold is quickly raised at the flow velocity of 1.1 liter per minute, and the mold is excessively heated. As a result, the sink mark and the capture occur.
In the conventional technique, the decrease in cooling ability as described above is dealt with the increase in amount of the cooling water to a great extent. However, when the amount of cooling water is increased, then the mold is in an excessively cooled state, and-the molten metal charged in the cavity is quickly cooled. Therefore, another inconvenience arises such that the misrun or the like takes place. For example, as depicted by the broken line (2)xe2x80x2 in FIG. 18, in the (N+3)th casting, the temperature of the mold is quickly lowered at the flow velocity of 1.6 liter per minute, and the mold is excessively cooled. As a result, the misrun occurs.
A general object of the present invention is to provide a method and an apparatus for cooling a mold, which make it possible to easily obtain an optimum casting quality in a stable manner by decreasing the contact surface area and the cooling volume of the cooling medium
A principal object of the present invention is to provide a method and an apparatus for cooling a mold, which make it possible to easily obtain an optimum casting quality in a stable manner by providing the directivity of cooling corresponding to the wall thickness of a cast product.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.